Convergent plate boundaries
(saw tooth - with the teeth on the side of the
over-riding plate) occur where two plates are colliding
together. Two continental plates will crumple and form
mountain ranges because neither is dense enough
to sink into the mantle. However, ocean plates will form
subduction zones as they sink back into the
mantle.

As the continent of
India collided with Eurasia, a shallow ocean between the two continents
subducted below Eurasia. Once the two continents touched, the subduction
stopped and the two continents crumpled together forming the highest
mountains in the world. Marine fossils high in the Himalayas are remnants
of that ancient ocean. Although volcanoes would have resulted from the
earlier subduction in the area, all volcanic activity has ceased since the
subduction ended. Shallow to moderate depth earthquakes and high, folded
mountains are characteristic of this continent-continent convergent boundary.

2. Continent - ocean Convergent Boundary

Shallow and deep
earthquakes, volcanoes, mountain building

When ocean plates collide with continental
plates, the denser ocean plate will sink or subduct beneath the continental
plate. As the ocean plate sinks into the mantle, an ocean trench
marks the start of subduction.
The sinking plate is cold and brittle and causes shallow to moderate to deep
earthquakes as it sinks lower down into the mantle. In fact, subduction
zones are the only localities on Earth where deep earthquakes
(300 to 700 km depths) occur. Temperature increases one degree Celsius for
each kilometer of depth. As ocean plates subduct, any water within the
ocean crust is eventually turned into steam. The rising steam melts the
crust and magma rises to the surface in these areas, forming volcanoes. The
Nazca plate subducting below the South American plate is a typical
subduction zone. An ocean trench
marks the start of subduction.
Volcanoes occur further to the east;
and earthquakes range from shallow
near the trench to deepest further
east where the ocean plate is deep within the mantle. Another example is
the Juan de Fuca plate subducting below the North American plate. Ocean
trenches, shallow to deep earthquakes and volcanoes characterize these
boundaries.

Example: West coast of South America, Pacific North-west as the Juan de Fuca
Plate subducts under the North American Plate

When two ocean
plates collide, one will subduct below the other. The start of subduction
is marked by an ocean trench
and shallow
earthquakes.
As the ocean plate subducts and any water in the rock turns to steam, the
rock above the steam will melt forming magma to rise and form volcanic
islands. Moderate to deep earthquakes mark the sinking of the subducting
plate into the mantle. If the subducting plate is large, a long trench will
mark the subduction zone and a line or arc of volcanic islands will be
formed. These are called volcanic island arcs.

Examples include
the Aleutian Island arc, the Philippine Island arc and the Japan Island
arc.